1. Field of the Invention
The invention relates to a system for controlling the attitude of a cylindrical body moving in a fluid, and more particularly to a system for controlling roll and its application to missiles. The roll-controlling system of the invention employs the fluid dynamic reaction forces set up by a rotating empennage.
2. Description of the Prior Art
In the text, the term "missile" is to be understood in its generic sense, which covers, inter alia, projectiles, rockets, and propelled or unpropelled missiles whose trajectory may or may not be controlled.
When a missile is moving in a fluid medium, either gas or liquid, it naturally tends to pivot about its longitudinal axis, also known as its roll axis, which axis is substantially coincident with the speed vector along the trajectory. This rotating movement is induced, when the missile is moving, by parasitic hydrodynamic or aerodynamic moments and/or thrust moments. These parasitic moments are due to constructional imperfections. The direction and magnitude of this rotational movement, or natural roll, are determined by the direction and magnitude of the resultant of the parasitic moments.
In certain missile firing applications, the attitude of the missile in roll needs to be positionally controlled and held by servo-control in a given direction, for example, when the missile is equipped with an auto-pilot or a military homing head. In other applications, on the other hand, it is desirable for the body of the missile to have imparted to it a rotary movement whose speed needs to be controlled within a more or less restricted range, for example, with the object of enabling a detector carried by the missile to operate at a known scanning frequency.
Techniques for controlling the attitude of missiles are widely known, in particular those which use aerodynamic control surfaces derived from the control surfaces of aircraft. Mention may be made of ailerons carried by the wings and canard control surfaces positioned at the front of the fuselage. A very different technique uses the reaction forces resulting from the expulsion of gases. These various techniques give rise to problems when the missiles are employed operationally in applications which involve special conditions of storage, handling and launching, in particular when this latter operation is performed from within a cylindrical tube or by gun-barrel effect.